postcss-less

PostCSS LESS Syntax

PostCSS Syntax for parsing LESS

Please note: poscss-less is not a LESS compiler. For compiling LESS, please use the official toolset for LESS.

Getting Started

First thing's first, install the module:

npm install postcss-less --save-dev

LESS Transformations

The most common use of postcss-less is for applying PostCSS transformations directly to LESS source. eg. ia theme written in LESS which uses Autoprefixer to add appropriate vendor prefixes.

const syntax = require('postcss-less');
postcss(plugins)
  .process(lessText, { syntax: syntax })
  .then(function (result) {
    result.content // LESS with transformations 
});

Inline Comments

Parsing of single-line comments in CSS is also supported.

:root {
    // Main theme color 
    --color: red;
}

Note that you don't need a custom stringifier to handle the output; the default stringifier will automatically convert single line comments into block comments. If you need to support inline comments, please use a custom PostCSSLess stringifier.

Rule Node

PostCSS Rule Node

rule.empty

Determines whether or not a rule contains declarations.

Note: Previously ruleWithoutBody. This is a breaking change from v0.16.0 to v1.0.0.

import postCssLess from 'postcss-less';
const less = `
    .class2 {
        &:extend(.class1);
        .mixin-name(@param1, @param2);
    }
`;
const root = postCssLess.parse(less);
 
root.first.nodes[0].empty // => true for &:extend 
root.first.nodes[1].empty // => true for calling of mixin

rule.extend

Determines whether or not a rule is nested.

Note: Previously extendRule. This is a breaking change from v0.16.0 to v1.0.0.

import postCssLess from 'postcss-less';
const less = `
    .class2 {
        &:extend(.class1);
    }
`;
const root = postCssLess.parse(less);
 
root.first.nodes[0].extend // => true

rule.important

Determines whether or not a rule is marked as important.

Note: This is a breaking change from v0.16.0 to v1.0.0.

import postCssLess from 'postcss-less';
const less = `
    .class {
        .mixin !important;
    }
`;
const root = postCssLess.parse(less);
 
root.first.nodes[0].important // => true 
root.first.nodes[0].selector // => '.mixin'

rule.mixin

Determines whether or not a rule is a mixin.

import postCssLess from 'postcss-less';
const less = `
    .class2 {
        .mixin-name;
    }
`;
const root = postCssLess.parse(less);
 
root.first.nodes[0].mixin // => true

rule.nodes

An Array of child nodes.

Note that nodes is undefined for rules that don't contain declarations.

import postCssLess from 'postcss-less';
const less = `
    .class2 {
        &:extend(.class1);
        .mixin-name(@param1, @param2);
    }
`;
const root = postCssLess.parse(less);
 
root.first.nodes[0].nodes // => undefined for &:extend 
root.first.nodes[1].nodes // => undefined for mixin

Comment Node

PostCSS Comment Node

comment.inline

Determines whether or not a comment is inline.

import postCssLess from 'postcss-less';
 
const root = postCssLess.parse('// Hello world');
 
root.first.inline // => true

comment.block

Determines whether or not a comment is a block comment.

import postCssLess from 'postcss-less';
 
const root = postCssLess.parse('/* Hello world */');
 
root.first.block // => true

comment.raws.begin

Precending characters of a comment node. eg. // or /*.

comment.raws.content

Raw content of the comment.

import postCssLess from 'postcss-less';
 
const root = postCssLess.parse('// Hello world');
 
root.first.raws.content // => '// Hello world'

Stringifying

To process LESS code without PostCSS transformations, custom stringifier should be provided.

import postcss from 'postcss';
import postcssLess from 'postcss-less';
import stringify from 'postcss-less/less-stringify';
 
const lessCode = `
    // Non-css comment
 
    .container {
        .mixin-1();
        .mixin-2;
        .mixin-3 (@width: 100px) {
            width: @width;
        }
    }
 
    .rotation(@deg:5deg){
      .transform(rotate(@deg));
    }
`;
 
postcss()
  .process(less, {
    syntax: postcssLess,
    stringifier: stringify
  })
  .then((result) => {
    console.log(result.content); // this will be value of `lessCode` without changing comments or mixins 
});